Removal of froth



July 23, l957 c. DJKSMAN ErAL y REMOVAL' oFA FROTH Filed April e. 19542,888,459 Fatented July 23, 1957 nEMovAL or Faoin-r Cornelis Dijksmanand Freerk J. Fontein, Heerlen, Netherlands, assignors to Stamicarbon N.V., Heerlen, Netlierlands Application April 6, 1954, Serial No. 421,363Claims priority, application Netherlands April 9, 1953 14 Claims. (Cl.252-321) The present invention relates to the treatment of liquidmaterial containing soluble albumen and air and more particularly to theseparating and breaking down of froth formed in such treatment. Morespecifically, the invention is concerned with separating and breakingdown the froth formed in the treatment of suspensions of grated andscreened potatoes.

As is well known, a considerable amount of difiiculty is experiencedfrom froth in the manufacture of potato starch. This is particularly soin those cases where the potatoes are grated with the addition of onlysmall amounts of water and then screened in centrifugal screens. In suchcases, the suspension formed has a high specific gravity and containsboth coarse and fine air bubbles. The bubbles are diflicult to removefrom the suspension; and upon removal, large quantities of stiff froth,which is diliicult to break down with conventional froth breakers, e.g., vacuum or other type, are formed.

Accordingly, the principal object of the present invention is to providea novel process and apparatus for eliminating the difficulties referredto above.

Further objects of the invention will also be apparent from thefollowing detailed description thereof.

The invention is based upon the discovery that the difficultiespreviously encountered in dealing with froth as abovementioned arewholly or mainly attributable to the presence together of fine andcoarse air bubbles. More specically, it has been found that if coarseand fine air bubbles (hereinafter referred to as coarse and fine froth,respectively) are removed separately from the liquid under treatment,such removal and the subsequent breaking down process are greatlyfacilitated.

Hence, the present method can be broadly described as comprising theremoval of the coarse and fine froth separately from the liquid materialundergoing treatment in two successive steps by first removing thecoarse froth and then the fine froth, and thereafter separately breakingdown the thus-removed coarse and fine froth. This method, as well asapparatus particularly adapted for carrying out the invention, are morespecifically described below.

According to the invention, the fine froth is preferably broken downwith the aid of a vacuum, while the coarse froth is broken down withouta vacuum by subjecting the same to shocks as, for example, by forcingthe froth against a plate or the like with a fan or equivalent means.

In the preferred manner of separating the froth, the liquid material,for example, a potato suspension containing coarse and fine froth, issupplied to a first zone or vessel from which it is continuouslydischarged at a lower level than the supply so as to establish adownward liquid current. At the same time, the rate of liquid supply anddischarge, and the liquid level, are so adjusted with respect to thecross-sectional area of the vessel, and depth thereof, respectively,that the fine froth moves downwardly and discharges from this first zonewith the liquid whereas the coarse froth builds up above 2 the liquidlevel and can be removed in de-watered condition from the top of thevessel.

The liquid discharged from the first zone, and now containing only finefroth, is then supplied to a second zone or vessel from which the liquiddischarge again takes place continuously at a lower level to establish adownward current. As in the first Zone, the rate of liquid supply andthe liquid level are adjusted with respect to the cross-sectional areaand depth of the vessel, respectively, so that the liquid dischargetherefrom is substantially free of air bubbles and the froth builds upat the top of the vessel in substantially de-watered conditions. Thisfroth is then passed to a froth breaker, preferably with the aid ofclean water, or at least water which is albumen-poor.

For the treatment of a suspension of grated and screened potatoes, it ispreferred to select the size of the first vessel iu relation to thesupply of material to be treated so that the suspension obtained from atleast hl. and no more than hl. of potatoes passes into the vessel perhour for every m.2 of the upper surface of the liquid in the vessel, theliquid level being from 2 m. to 2.5 m. below the overflow brim of thevessel, i. e., the froth overflows from said zone at from 2 m. to 2.5 m.above the liquid level in the zone.

For the second zone or vessel, it is preferred that this be dimensionedto give an upper liquid surface of such area that suspension from notmore than 20 hl. of potatoes passes into the vessel per hour for everym.2 of such surface, the overflow brim for the fine froth being from 2m. to 2.5 In. above the liquid level. Thus, in this embodiment, theliquid surface area in the second vessel in which the tine froth isseparated off is at least four times as large as the surface of theliquid in the first vessel in which the coarse froth is separated off.Preferably, it is five to six times as large.

The invention is more specifically described below by reference to theaccompanying drawing which diagrammatically shows a preferred apparatusfor carrying out the purposes of the invention.

The apparatus shown includes a potato grater 1, a centrifugal screen 2,a tank 3 for separating olf coarse froth, means l for breaking thecoarse froth, a pressure pump 5, a vessel 6 for separating off finefroth, means 7 for breaking the fine froth, a suction pump 8, and aliquid tank 9. Conduits 10 to 19 connect the aforementioned deviceswhile the elements 20 and 21 represent valves in conduit 12 and theliquid discharge from tank 6, respectively.

ln use, potatoes and water are supplied to the grater l, at a and b,respectively. Water is also supplied at c to vessel 6. At d, the coarsecomponents, mainly fibers, separated off in centrifugal screen 2, aredischarged, while the discharge of the de-frothed potato starchsuspension and of the air takes place at e and at f and g, respectively.

In the grater 1, the potatoes are finely grated and mixed with water,thusproducing a suspension consisting essentially of starch particles,fibers, and slightly diluted fruit water. For this grating operation, agrater as described in German patent specification No. 188,153 may beused. Subsequently, the fibers are separated, as indicated above, at dfrom screen 2. The latter is preferably a centrifugal screen asdescribed in British patent specification No. 681,043 since with such ascreen the fibers can be removed in a highly de-watered state.

ln separating off the fibers, in the manner described above, aconsiderable amount of froth is formed in the suspension. Accordingly,the suspension and associated froth are subsequently conveyed fromscreen 2 to tank 3 by means of conduit 11. Tank 3 is open at the top,for a purpose hereinafter apparent, and serves as the first zone inwhichthe coarse froth is removed.

The liquid level in tank 3 is kept a little above the mouth of feedopening 23 and preferably about 21/2 rn. below the overow bri-m 24through suitable regulation of discharge valve 20. A trough 25, providedaround tank 3, collects whatever coarse froth 35 overflows, the thus,-collec'ted froth being fed through conduit 14 to froth breaker 4. Y k

As illustrated, the discharge aperture 26r of tank 3is positioned nearthe bottom of the tank. Consequently,- the suspension in tank 3 tiowsdownwardly and bubbles of froth above a certain general size rise whilebubbles below such size go along with the downwardly owing suspension. Y

Above liquid level 22, the coarse froth is de-watered to such an extentthat the froth which flows over into collecting trough 25 can be brokendown without difficulty in froth breaker 4. As shown, the froth breakeris of conventional type and includes an encased fan 4 which is soconstructed that it forces the froth against a plate 27 positionedwithin discharge passage 41 'thus breaking down the froth. The liquidthus removed in froth breaker 4 is then returned to the tank 3, at apoint above the level 22 of the liquid therein, by means of conduits 15and 19. Air liberated from the froth is discharged through an aperture gprovided in discharge passage 41. I

- The cross-sectional area of tank 3 is, for example, one square meterper hundred hl. of potatoes treated per hour. The choice ofcross-sectional area is of importance,- for if it is too small withrespect to the quantity of froth in the vessel at any particular time,coarse froth is insuiiiciently separated from the suspension. On theother hand, if this cross-sectional area is too large, the tank is tooexpensive. In addition, further diiiculties might be caused by rising oftine froth in the tank along with the coarse froth. l

In connection with the preceding, it is to be noted that it is thequantity of potato passing through the tank in a given time whichdetermines the selection of the appropriate dimensions for the tank. Thequantity of water employed, i. e., the concentration of the suspension,is of secondary importance in this connection since although the use,for example', of larger quantities of water involves a higher rate ofpassage of the suspension through the tank at a given rate of treatmentof the potato content, it is found that the velocity at which froth isseparated offl is about inversely proportional to the concentration ofthe suspension. The depth of tank 3 in rela tio'n to the suspensionlevel is also an important factor and should be such that the overowingfrothis sufficiently de-water'ed, since the presence in the froth of toolarge an amount of albumen is a hindrance to breaking down the froth.The liquid discharged from the rst zone (tank 3) and free of coarsefroth, is fedby means ofhvalve 20, conduits 12 and 13, and pump 5 to thesecond treating zone, namely, closed tank 6, for removal of the finefroth therefrom. Since the frothy liquid fed to tank 6 is difficult topump, pump should be amply dimensioned. The liquid level 28 in lvessel 6is kept close above the plate 29, which is fixed in the vessel,6 by therods 30. The, outlet opening 31 of conduit 13 is disposed close aboveplate 29, so that currents which Awould interfere with the rising of thesmall froth bubbles are avoided. In the top of vessel 6, an overflowfunnel 32 is provided whose brim 33 is abou 21/2 m. above the level ofthe liquid. Over the overflow funnel 32 there is a sprayer 34 which isprovided with water through c for a purpose hereinafter discussed. v

The cross-sectional area of the vessel 6 is over one rn.2 per 20 hl. ofpotatoes treated per hour. Hence, the sectional area of vessel 6 isyabout tive times as large as the sectional area of tank 3. This area isneeded for realizing a complete separation of the fine froth 36 from thesuspension. On its way from the liquid level 28 to the brim of thefunnel, which is 21/2. rn. higher, the ne 4 froth is de-watered, withthe result that only a negligible amount of soluble albumen is lefttherein. It will be appreciated that distances of less than theabovementioned 21/2 m. between the liquid level and brim 33 of funnel 32can also be used although, for best operations, the distance is asspecifically stated.

The de-frothed starch suspension is discharged at e through dischargeopening 40. On the other hand, the ine froth, which gets into the'funnel 32, is led into the froth breaker 7 via conduit 16, by means ofthe water issuing from sprayer 34 and under the influence of thedepression generated by vacuum pump 8. Froth breaker 7 comprises aclosed vessel 37, connected at its upper end with pump 8 by means ofconduit 17 and at its lower end with tank 9, by conduit 18. As shown,the discharge opening 3S connecting tank 9 with conduit 19 is higherthan the bottom opening of conduit 18, so that a water seal is formed intank 9.

Conduit 16 ends in a nozzle 39, which is positioned within vessel 37 andterminates adjacent a wall thereof. As a result, the froth flows out ofnozzle 39 against the wall at a high speed, thus being broken down.Froth breakdowni is also promoted by the depression prevailing in vessel37. The liquid recovered in this manner flows back into tank 3 through,conduit 18, tank 9, and conduct 19. Air separated off is discharged at fby pump 8; via conduit 17.

With an arrangement as above described, the capacity of pump 8 shouldbey at least one m.3 of moist air per 2 hl. of potatoes treated perhour. This pump 8 also serves to maintain the pressure in vessel 37 at amaximum of about 0.9 kg./cm.2, tank 9 being situated suiliciently lowerthan the vessel 37 to maintain this depression.

It will be appreciated that various modifications may be made in theinvention as described herein without in any way deviating therefrom.Hence, the invention is not limited by the foregoing description andshould be determined by the scope of the following claims wherein weAclaim: Y y

l. In the treatment of a liquid material containing soluble albumen andair by a process involving the continuous formation of both coarse andfine froth, removal of said froth from the liquid material andsubsequent breaking down of the removed froth, the improvement whichcomprises removing the coarse and fine froth separately from said liquidmaterial invtwo successive zones by first removing said coarse froth inone zone and then removing said line froth in thel other zone andthereafter separately breaking down the thus-removed coarse froth andfino froth by forcing both said coarse froth and said tine froth againsta rigid surface.

2. The process of claim l wherein the tine froth is broken down byforcing same against a rigid surface while maintaining said `froth underreduced pressure.

3. The process of claim l wherein the removal of froth in each zoneiselfected by continuously supplying the liquid material to bede-frothed to said zone, continuously discharging said materialtherefrom at a lower level than the supply whereby a downward liquidcurrent is established and the froth to be removed rises in said zone,and overflows therefrom in de-watered condition.

4. The process of claim l wherein the removal of froth in each zone iseffected by continuously supplying the liquid material to' bede-'frothed to' said zone, continuously discharging said materialtherefrom at a lower level than the supply whereby a downward liquidcurrent is established Aand the froth to be removed rises in said zone,and overflows therefrom in de-watered condition at a distance of from 2m. to 2.5 m`. above the liquid level in the zone.

5. The process of claim l wherein the removal of froth in each zone iseffected by continuously supplying the liquid material to be de-frothedto said zone, continuously discharging said material therefrom at alower level than the supply whereby a downward liquid current isestablished and the froth to be removed rises in said zone, and

overflows therefrom in de-watered condition at a distance ofsubstantially 2.5 rn. above the liquid level in the zone.

6. The process of claim l wherein the fine froth removed from the otherzone is conveyed to the breaking down step with water which isalbumen-poor.

7. The process of claim 3 wherein the liquid material treated is asuspension of grated and screened potatoes.

8. The process of claim 3 wherein the liquid material treated is asuspension of grated and screened potatoes, said suspension is suppliedto the first zone at the rate of at least 80 hl. and not more than 120hl. of potatoes, per hour, for each m? of the liquid surface in saidzone and said coarse froth is removed by overow from said zone at from 2rn. to 2.5 m. above the liquid level in said zone.

9. The process of claim 8 wherein said suspension with coarse frothremoved therefrom is supplied to the second zone at the rate of no morethan 20 hl. of potatoes, per hour, for each 111.2 of the liquid surfacein said zone and said fine froth is removed by overflow from said Zoneat from 2 m. to 2.5 m. above the liquid level in said zone.

10. Apparatus for removing and separating froth from liquid materialscontaining same which comprises a first vessel adapted to remove coarsefroth from said liquid material while leaving the fine froth therein, asecond vessel adapted to remove ne froth from said liquid material afterremoval of the coarse froth therefrom, each of said vessels having aliquid inlet and an outlet with the outlet of the first vesselconnecting with the inlet of the second whereby liquid material may besuccessively passed therethrough, the outlet of each vessel beinglocated below the inlet thereof whereby liquid material passingtherethrough has a downward current and froth, coarse in said rst vesseland fine in said second vessel, rises upwardly in the vessel andoverflows therefrom, separate overflow means associated with each ofsaid vessels for collecting the froth rising therein and overflowingtherefrom and separate froth breaking means operatively connected witheach vessel for separately breaking down coarse and fine froth, each ofsaid last mentioned breaking means comprising a rigid surface and meansfor forcing the froth against said surface.

11. Apparatus as claimed in claim 19 wherein the means for breaking downsaid coarse froth includes an encased fan having a plate associatedtherewith against which said froth is driven by said fan and the meansfor breaking down said fine froth comprises an at least partiallyevaporated Vessel and means for forcing said fine froth against a wallof said vessel.

12. Apparatus as claimed in claim 10 wherein each of said overflow meansis positioned to receive froth overflow from 2 to 2.5 m. above the levelof liquid material passing through said vessels.

13. Apparatus as claimed in claim l0 wherein the overllow meansassociated with said second vessel includes an overflow funnelcommunicating with the froth breaking means operatively connected withsaid second vessel, said funnel having a froth inlet within said vessel,and water spraying means positioned over said inlet to assist in feedingfroth within said funnel to said froth breaking means.

14. Apparatus as claimed in claim 10 wherein the cross-sectional area ofsaid second vessel at the level of the inlet thereof is at least fourtimes as great as the corresponding area of said first Vessel.

References Cited in the le of this patent UNITED STATES PATENTS1,176,428 Callow Mar. 21, 1916 2,353,833 Kimmell July' 18, 19442,471,571 Kimmell May 31, 1949 2,478,150 Young Aug. 2, 1949 2,765,867Revallier et al Oct. 9, 1956 U. S. DEPARTMENT OF COMMERCE PATENT OFFICECERTIFICATE OF CORRECTION Patent No., 2,800,459 July 23, 1957 CornelisDijksman et al.,

It is hereby certified that error appears in the printed specificationof' the above numbered patent requiring correction and that the saidLetters Patent should read as `corrected below.

Column 6, line 1l, for uevaporated read evacuumed@-n Signed and sealedthis 25th dey of March 1958.

(SEAL) Attest: KARL H. AXLINE ROBERT C. WATSON Attesting OfficerComissioner of Patents

1. IN THE TREATMENT OF A LIQUID MATERIAL CONTAINING SOLUBLE ALBUMEN ANDAIR BY A PROCESS INVOLVING THE CONTINUOUS FORMATION OF BOTH COARSE ANDFINE FROTH, REMOVAL OF SAID FROTH FROM THE LIQUID MATERIAL ANDSUBSEQUENT BREAKING DOWN OF THE REMOVED FROTH, THE IMPROVEMENT WHICHCOMPRISES REMOVING THE COARSE AND FINE FROTH SEPARATELY FROM SAID LIQUIDMATERIAL IN TWO SUCCCESSIVE ZONE BY FIRST REMOVING SAID COARSE FROTH INONE ZONE AND THEN REMOVING SAID FINE FROTH IN THE OTHER ZONE ANDTHEREAFTER SPARATELY BREAKING DOWN THE THUS-REMOVED COARSE FROTH ANDFINE FROTH BY FORCING BOTH SAID COARSE FROTH AND SAID FINE FORTH AGAINSTA RIGID SURFACE.